Ball-point pens are well known and widely used as writing tools, and each comprises a writing ball rotationally held in a penpoint tip. An ink filled in an ink reservoir fixed in the ball-point pen will be guided in use to the writing ball so as to be transferred to a paper sheet, or the like, as the ball rotates. Usually employed as a material for forming writing balls in ball-point pens are zirconia, stainless steel or tungsten.
Recently, some types of novel aqueous ink compositions have been proposed, and bright pigments contained therein have been intended to give golden, silver-colored or any other metallic-colored writings. For example, an aluminum pigment containing aqueous ink is disclosed in the Japanese Patent Laying-Open Gazette Hei No. 7-118592. A pearl-glossy pigment containing aqueous ink is disclosed in the Japanese Patent Laying-Open Gazette Hei No. 8-151547. An aqueous metallic-colored ink disclosed in the Japanese Patent Laying-Open Gazette Hei No. 11-29734 comprises an aluminum pigment whose particles are coated with an organic pigment particles by means a fixing agent.
However, it has not necessarily been easy to achieve sufficiently intensive brilliancy and stereoscopic feeling in the writings or membranes formed of such prior art aqueous inks containing the afore-said aluminum pigment or pearl-glossy pigment. Further, a resin material or the like used to fix a colorant (viz., dyestuff molecules or pigment particles) on the described basic pigment to realize a metallic luster has also caused a poor brilliancy.
In view of these problems, the present applicant has already proposed in its Japanese Patent Application No. 11-76868 an improved type of brilliant aqueous ink composition. This composition was characterized by a glass flake pigment that would provide, in addition to brilliancy higher than those given by any known aqueous inks comprising conventional pigments, an intensive stereoscopic feeling that had not been realized by the prior art aqueous inks.
Particle diameter of such a glass flake pigment is comparatively large so that a higher viscosity of ink would possibly cause certain incontinuity in the writings, if the known ordinary writing ball were used.